Several methods for the preparation of metal borides are known including direct synthesis from the elements, reduction of mixtures of metal oxides and boron oxide by carbon, reduction of metal oxides with boron carbide and carbon, and reduction of mixtures of metal halide and boron trihalide by hydrogen. Each of these requires high temperatures, in excess of about 1200.degree. C., usually near 2000.degree. C.
More recently metal borides have been synthesized by thermal decomposition of gaseous metal borohydrides at lower temperatures. Titanium diboride, zirconium diboride and hafnium diboride thin films were obtained by using gaseous chemical vapor deposition at about 200.degree. C. of the respective tetrahydroborate precursors; see Jensen, J. A., et al., J. Am. Chem. Soc., 110, 1643-1644 (1988).
The synthesis of zirconium boride, ZrB.sub.2, from zirconium borohydride, Zr(BH.sub.4).sub.4, was explored by a variety of methods including gaseous chemical vapor deposition in a hot tube, laser chemical vapor deposition with both continuous-wave and pulsed lasers, and continuous-wave laser synthesis of fine powders. Products made at high temperature contained excess boron, while those made at low temperature were boron deficient. The gaseous chemical vapor deposition and laser chemical vapor deposition techniques using zirconium borohydride were deemed more promising than older conventional techniques and were considered predictive of the behavior of hafnium borohydride and titanium borohydride; see Rice, G. W., J. Am. Ceram. Soc., 71(4), C-181-C-183 (1988).
Wayda, A. L., et al., Appl. Phys. Lett., 53, (5), Aug. 1, 1988, reported deposition on various substrates of films of zirconium and hafnium borides by the low temperature (100.degree.-270.degree. C.) thermal decomposition of gaseous M(BH.sub.4).sub.4 wherein M is zirconium or hafnium. The resultant films were characterized as having favorable mechanical and electronic properties with only surface oxide contamination. Thus the metal borohydrides were considered to be excellent precursor complexes for vapor phase thermal decomposition to yield metal boride films.
These prior art techniques for generation of the metal borides involve deposition from the gas phase, such as chemical vapor deposition or laser vapor deposition. The deposition of metal boride precursors from solution at ambient pressure is easier to practice than gas phase routes and could prove to be less expensive.
It is therefore an object of the present invention to provide processes for deposition of metal boride precursors from the solution phase. It is a further object of the present invention to provide novel metal boride precursor complexes. It is a further object of the present invention to provide metal borides from these novel precursor complexes.